Representing the Logic of Statutory Rules in the United States

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1 MANUSCRIPT PREPUBLICATION VERSION FOR OTHER SCIENTISTS ONLY; FOR NON-COMMERCIAL INTERNAL AND EDUCATIONAL PURPOSES ONLY (forthcoming chapter in Logic and Legislation (Michał Araszkiewicz and Krzysztof Płeszka, eds.), in Springer Series Legisprudence Library (Luc Wintgens and Daniel Olivier-Lalana, eds.)(2015)) Chapter 13 Representing the Logic of Statutory Rules in the United States Vern R. Walker Director, Research Laboratory for Law, Logic & Technology; Maurice A. Deane School of Law, Hofstra University, New York Telephone: Bernadette C. Lopez Research Laboratory for Law, Logic & Technology; Maurice A. Deane School of Law, Hofstra University, New York Matthew T. Rutchik Research Laboratory for Law, Logic & Technology; Maurice A. Deane School of Law, Hofstra University, New York Julie L. Agris Hofstra North Shore-LIJ School of Medicine, Hofstra University, New York; Research Laboratory for Law, Logic & Technology, Maurice A. Deane School of Law, Hofstra University, New York Abstract This chapter presents one method of representing the logical structure of systems of legal rules, as they are established by statute in the United States. The chapter uses default logic and rule trees to reflect the dynamic and pragmatic context in which legal rules are used, as well as the interplay among legal rules, policy objectives and evidence. Rule trees also capture such important substructures as relevant-factor rules and legal presumptions. They are also operational structures available for software computation or for exchange in digital form, and help legal practitioners organize evidence and arguments. Examples throughout are drawn from the statute governing the Vaccine Injury Compensation Program (VICP), which provides compensation to persons who have sustained vaccine-related injuries. Although the examples are from this particular statute, the

2 2 default-logic framework is applicable to any other statute in the United States and to those in many other jurisdictions. Keywords legal rules, default logic, rule systems, governmental decision-making, evidence assessment 13.1 Introduction In the United States as elsewhere, statutes contain the basic legal rules established by the legislative branch of government. This chapter focuses on the dynamic and pragmatic aspects of such legal rules, and of the systems of legal rules that statutes create. One challenge for logical analysis is to represent systems of rules in such a way that the dynamic processes by which they are created and which they create in turn are reflected in the analysis. Similarly, the representation should reflect the pragmatic nature of rule systems being used to orchestrate decision processes in real time, with limited resources and limited information. To the extent that a logical representation succeeds in reflecting this dynamic and pragmatic context, it is also likely to be practical that is, of everyday use to participants in legal proceedings. In this chapter, we describe the core structure of such a logical representation The Rule of Law, Processes, and Systems of Rules The rule of law requires governmental action (and sometimes inaction) to be justifiable (MacCormick 2005, pp ; Walker 2007b, pp ). In the United States, a primary goal in enacting any statute is to control the use of governmental power by setting up complex processes that constrain the discretion of governmental actors when they take actions. For example, statutes may prescribe procedural and substantive conditions under which an administrative agency is authorized or required to issue legislative rules, or they may prescribe conditions under which a court is required to order compensation for a plaintiff. As a result, statutes create or presume decision-making processes for types of governmental action. Broad types of governmental action (such as legislating, enforcing, or adjudicating) are typically processes made up of numerous constituent actions. For example, issuing a valid legislative rule might involve official publication of notice, taking testimony at a hearing, and official publication of the agency s reasoning. Issuing a valid judicial judgment ordering compensation might involve serving notice on a defendant, filing and deciding motions, and conducting a trial. A primary

3 3 goal of many statutes is to prescribe conditions for lawfully conducting a process leading to an ultimate governmental action. Different participants often play different roles with regard to distinct logical components of the decision process. For example, in the process of legislative rulemaking, various actors, such as agency officials, the potentially affected members of the public, and the courts, may all play different roles. Parties and intervenors, witnesses, judges and juries may all play different roles in the process of judicial adjudication. With respect to each decision or action within a process, a statute may state not only the substantive conditions under which the governmental action (or inaction) is required, permitted, or prohibited, but also the process conditions (both procedural and evidentiary) for making the decision lawfully. This section of the chapter discusses three logical components of such processes, and then describes a formal system for representing systems of legal rules applicable to decisions about those components. As an example of the U.S. statute, this chapter will use the National Childhood Vaccine Injury Act of 1986 ( Vaccine Act ), which sets up the Vaccine Injury Compensation Program (VICP). 1 The VICP is a hybrid administrative-judicial system in the United States that provides compensation to persons who have sustained vaccine-related injuries (Walker 2009; Walker et al. 2013). 2 Petitioners seeking compensation file claims in the Court of Federal Claims. If the Secretary of the Department of Health and Human Services (HHS) contests a claim, a special master within the Court of Federal Claims decides whether it is meritorious. Contested VICP cases often involve complex issues of fact about causation e.g., whether the vaccine played a causal role in bringing about the injury. Such factual adjudication by special masters requires taking into account medical, scientific, and other expert evidence, along with the non-expert evidence, and the decisions of special masters include findings of fact and conclusions of law. 3 These decisions are subject to review by the Court of Federal Claims, whose judgments are in turn appealable to the Court of Appeals for the Federal Circuit. 4 This statute provides illustrations of the logical structure that we describe in this chapter U.S.C. 300aa-10(a) (2011). 2 Compensation awards are paid out of the Vaccine Injury Compensation Trust Fund, which is funded by an excise tax on each dose of covered vaccine. See 26 U.S.C (2012), and 42 U.S.C. 300aa-15(i)(2) (2011) U.S.C. 300aa-12(d) (2011) U.S.C. 300aa-12(f) (2011).

4 Logical Components within Governmental Decision-Making Processes Statutorily created processes leading to governmental action typically involve three major types of logical components: policy objectives, legal rules, and evidence (Walker et al. 2013). Instances of these major components play roles in different types of decisions or actions. For example, policy objectives can be adopted by governmental actors, used to justify or argue against governmental actions, and promoted or undermined by such actions; legal rules are established, modified, and applied; evidence is admitted into the record of a proceeding or excluded from the record, and is used to warrant findings of fact. In general terms, policy objectives help to justify adopting or modifying legal rules, and help guide the application of those rules in particular cases, in accordance with the evidence. Distinguishing these types of logical components allows the structuring of complex processes for making decisions, in which different participants perform different tasks with respect to different decisions or actions. For example, the major governmental decision makers in the VICP include the United States Congress, the Secretary of HHS, the Supreme Court of the United States, the United States Court of Appeals for the Federal Circuit, the United States Court of Federal Claims, and special masters attached to the Court of Federal Claims. These participants have different roles to play with respect to different decisions regarding the different types of logical components. For example, Congress established the fundamental policy objectives for the VICP, and the statutory legal rules that are fundamental to the claims process in the VICP, while administrative agencies can create certain additional types of rules, and reviewing courts interpret and elaborate all of those rules. Special masters function as factfinders by assessing the evidence in particular cases and making findings of fact; the Court of Federal Claims provides a first level of review of those findings; and the Court of Appeals and the Supreme Court provide appellate review. The actions of each decision maker are governed by systems of legal rules, some of which are constitutional in origin, but far more are statutory. Having different participants perform different actions with respect to different logical components within a single process means that different institutions can have the particular structures and competences needed to perform the particular tasks assigned. For example, the political nature of Congress is optimal for negotiating and striking the trade-offs needed in balancing competing policy objectives; the experience of appellate court judges is best fitted for interpreting statutory language, formulating legal rules, and combining those rules into complete and consistent systems; and the experience of special masters in deciding a high number of vaccine cases prepares them for assessing the credibility of the expert witnesses who appear in such cases. Distinctions such as that between issues of law (to be decided de novo by reviewing courts) and issues of fact (to be judicially reviewed under a deferential standard) are made in rules designed to ensure that par-

5 5 ticular institutions with particular competences play suitable roles, and do not encroach upon the decisional role of another institution. Moreover, institutions with different structures, competences and missions can collectively provide a process that has internal checks and balances among the different participants. For example, reviewing courts can ensure that special masters understand and correctly apply the legal rules, while special masters can ensure that the evidence in each particular case receives individual treatment under those rules. Policy Objectives. Within the framework of principles established by the United States Constitution (such as due process and equal protection), 5 Congress adopts particular policy objectives for any particular statutory program, and participants within the decision-making processes established for that program are expected to pursue those policies when implementing the program. The structure of the process ensures that only certain participants have policy-making authority outright, while other participants can implement and balance policies when performing other decision-making tasks. For example, Congress established the fundamental policy objectives specific to the VICP, including increasing the supply of vaccine manufacturers and decreasing the cost of vaccines, 6 as well as promoting the use of vaccines and providing an effective and efficient compensation system for those injured by vaccines (Binski 2011, pp , ; Meyers 2011, p. 794; Grey 2011, pp ; Currier 2009, pp ). Various participants are responsible for implementing these Congressional objectives in their activities, for example: the Secretary of HHS as the party respondent in the adjudication of particular claims, the reviewing courts in interpreting statutory provisions, and the special masters when they issue findings of fact and conclusions of law in particular cases. The Secretary and the appellate courts can also implement policies that are more generic than the VICP, such as administrative efficiency. Moreover, the adjudication processes all share the same epistemic policy : to produce determinations of fact that (1) are as accurate as possible and (2) are warranted by the legally available evidence (Walker 2003). Legal rules. Legal rules are essential means for achieving the rule of law, because they make the justification of governmental action more transparent, as well as help ensure that similar cases are decided similarly (Walker 2007a, pp ; Walker 2007b, pp ). For example, in the vaccine compensation process, legal rules play a central role in deciding whether the vaccination played a causal role in bringing about the person s injury or death. Congress created the core causation rules in the statute (discussed in Section 3 below), the Secretary can add to those rules by amending the Vaccine Injury Table, and the appellate courts add more explicit rules when they decide cases. Decisions by the Court of Federal Claims do not create legal rules binding on other decisions of the same court on 5 U.S. Constitution, Amendment H.R. Rep , 1986 U.S.C.C.A.N. 6344, (26 September 1986).

6 6 other claims, 7 nor do decisions by special masters create rules binding on other special masters. 8 Thus, the process ensures that the governmental institutions that have rule-creating authority have the experience and competence to create rules that appropriately balance competing epistemic and non-epistemic policies. As discussed in Sections 3 and 4 below, legal rules are either substantive or process rules, with the latter category including both procedural rules and evidentiary rules. Evidence. As Section 2.2 discusses, legal rules determine what issues of fact are relevant to any particular decision-making process, by identifying the situations that will satisfy the rule requirements. One or more participants in a process will be responsible for assessing the evidence and deciding whether or not the rule conditions have been met. In vaccine compensation cases, for example, the special master assesses the probative value of the evidence and makes findings of fact and conclusions of law concerning causation. 9 The Court of Federal Claims may set aside those findings of fact only if they are arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law. 10 If the Court of Federal Claims does set aside a special master s finding of fact, then the Court may either issue its own findings of fact or remand the petition to the special master for further action in accordance with the court s direction. 11 In keeping with the general rule that appellate courts decide de novo only issues of law, not issues of fact, the standard of review in the Court of Appeals for the Federal Circuit is that the Court uphold[s] the Special Master s findings of fact unless they are arbitrary or capricious West Coast General Corp. v. Dalton, 39 F.3d 312, 315 (Fed. Cir. 1994) ( Court of Federal Claims decisions, while persuasive, do not set binding precedent for separate and distinct cases in that court. ); Ains, Inc. v. United States, 365 F.3d 1333, 1336 n. 1 (Fed. Cir. 2004) ( CFC [Court of Federal Claims] holdings, like those of federal district courts, are instructive but not precedential, and do not bind future court rulings. ). 8 Graves v. Secretary of the Department of Health and Human Services, 101 Fed. Cl. 310, 332 (Fed. Cl. 2011) ( Special masters are not bound by decisions of other special masters. ) U.S.C. 300aa-12(d)(3)(A)(i) (2011) U.S.C. 300aa-12(e)(2)(B) (2011); Stotts v. Secretary of the Department of Health and Human Services, 23 Cl. Ct. 352, (Ct. Cl. 1991) U.S.C. 300aa-12(e)(2)(B)-(C) (2011). 12 Carson ex rel. Carson v. Secretary of Health and Human Services, 727 F.3d 1365, 1368 (Fed. Cir. 2013).

7 Representing Action-Oriented Systems of Legal Rules The logic used to represent legal rules must allow for the dynamic and pragmatic nature of rule-based legal reasoning. Legal reasoning is pragmatic in at least three senses. First, the ultimate subject matter of such reasoning is decisionmaking leading to governmental action. The ultimate focus on whether or not to engage in some action gives the rule-based reasoning a pragmatic focus. Second, legal decision-making occurs in real time, uses limited resources, and is usually based on incomplete information it is decision-making under uncertainty (Kahneman et al. 1982; Morgan and Henrion 1990). Thus, rule-based legal reasoning is constrained by pragmatic circumstances. Third, legal reasoning balances the epistemic objective of law against the applicable non-epistemic objectives (Walker 2003, p. 132). The epistemic objective is to produce determinations of fact that (1) are as accurate as possible and (2) are warranted by the legally available evidence. Weighed against this epistemic objective are numerous nonepistemic objectives for example, procedural fairness, administrative efficiency, or adequate vaccine production. One function of a system of legal rules is to strike the appropriate balance between the epistemic objective and the applicable nonepistemic objectives. Given these three dimensions in which legal reasoning must be pragmatic, it is no surprise that the logic of legal reasoning generally goes well beyond deductive logic, and incorporates abductive logic (Josephson and Josephson 1996) and nonmonotonic logic (Brewka et al. 1997; Kyburg and Teng 2001, pp ; Levi 1996, pp ; Prakken 1997, pp ), as well as scientific reasoning, decision theory, risk analysis, risk-benefit analysis, and other methodologies that can adequately capture rule-based and policy-based reasoning. The topic of this chapter, however, is representing the logic of statutory rules, which is in many ways more straightforward than representing the logic of either evidence assessment or policy-based reasoning. Evidence assessment is the process of reasoning from the evidence in the legal record of a proceeding to findings about whether the governing rule conditions are satisfied in a particular case. Evidence assessment might well require nonmonotonic logic and scientific reasoning. Policy-based reasoning is the process of determining whether a particular rule or factual finding is prudent or justifiable, when measured against the applicable policy objectives. Policy-based reasoning often requires decision theory, risk analysis, and risk-benefit analysis. By contrast, the representation of statutory legal rules generally requires only default logic, of the kind discussed next. By default logic, we mean the logic of default reasoning. Default reasoning employs presumptive inference rules and the available evidence to warrant default or provisional conclusions, which are subject to revision on the basis of defeating evidence and default logic formalizes such reasoning (Brachman and Levesque 2004, pp ; Kyburg and Teng 2001, pp ; Brewka et al. 1977, pp ; Poole 1988; Reiter 1980). Default logic has a presumptive or prima facie quality that is well suited for representing legal reasoning whether reasoning within

8 8 the system of legal rules itself, or evidence assessment applying those rules to particular cases, or policy-based reasoning about legal rules or findings. In the case of a system of legal rules, the default quality shows up primarily in two ways. First, the rule system may formally contain explicit defeaters propositions that act to defeat an otherwise valid line of reasoning or support (Pollock 1990, p. 79; Brewka et al. 1997, pp. 2-3, 16; Prakken et al. 2003, pp. 32, 37-38; Prakken and Sartor 2004, pp ; Prakken and Sartor 1997, p. 3; Walker 2007a, pp , ). In law, such explicit defeaters are found in the form of exceptions to a rule or as an affirmative defense to a claim. Second, the rule system itself is generally open to revision for example, by interpreting or defining a legal phrase in an existing rule (thereby creating a new rule) or by creating an exception to an existing rule. We will see examples of all of these variations in the rules governing the VICP. First, however, we will sketch the semantic elements of a formal representation of a legal rule, and of a system of legal rules. A single legal rule is a conditional proposition, such as if p, then q, with a single q as the conclusion and one or more propositions as the condition(s) (Brewer 1996, p. 972). Whenever multiple conditions are present, they are connected to the conclusion by one of three logical connectives: AND (the conclusion is true if, but only if, all connected conditions are true); OR (the conclusion is true if, but only if, at least one of the connected conditions is true); or RULE FACTORS (the listed conditions are relevant in determining whether the conclusion is true, but the rule specifies no algorithm or formula for assigning a truth-value to the conclusion as a function of the truth-values of those conditions). Graphical depictions of these three possibilities are shown in Figure Fig Graphic Representation of Rule Forms with Logical Connectives AND, OR, and RULE FACTORS

9 9 Every proposition in a rule has one of three truth-values: true / undecided / false. The conclusion is dependent for its truth-value upon the truth-values of its rule conditions. This three-valued logic captures the dynamic nature of legal proof. For example, when any particular vaccine-compensation proceeding begins, all propositions in the rule tree are undecided. The parties might stipulate some propositions as true or false, with the remainder being contested issues. The parties then produce evidence on those contested issues and try to persuade the special master (as factfinder) to make favorable findings of fact on the contested rule conditions. When the factfinder makes findings of fact about a rule s conditions, the rule s logical connective determines the truth-value of the conclusion (with the exception of the RULE FACTORS connective, as noted above). Expressed generally, a legal rule identifies the propositions that are relevant to proving the rule s conclusion, and may determine a truth-functional logical connective for multiple conditions, but a particular proceeding to apply that rule begins with the decision maker being neutral on whether the conditions for applying the rule are satisfied or not. When a rule states an exception or an affirmative defense, the condition is a defeating proposition for the conclusion, and the logical connective is UNLESS. UNLESS has the meaning of but not if : if the defeating condition is true, then the conclusion is false, even if the main prima facie conditions for establishing that conclusion are true. The rule conditions that would determine the truth-value of the conclusion in the absence of a defeater constitute the prima facie case for the conclusion. Thus, a true defeater trumps or overrides the prima facie proof, by dictating that the conclusion must be false. A defeater relation can be depicted graphically as in Figure Fig Graphic Representation of Rule Form with Logical Connective UNLESS Of course, representing particular statutory provisions might warrant the use of additional or different logical connectives (e.g., exclusive OR) or logical operators (e.g., negations), but several considerations advise caution. Occam s razor or the principle of parsimony cautions against adding connectives unnecessarily, especially those not readily intuitive to humans. Using unnecessary and unintuitive distinctions in representing statutory text is likely to increase the cost of the resources needed to extract the logical structure (e.g., the time needed to resolve alternative logical representations, or the computation needed to automatically extract that

10 10 structure) and to increase the risk of error (inaccuracy in representing the logic of statutory provisions). Moreover, in a many-valued logic system, even seemingly simple logical concepts such as negation may result in numerous logical operators (Gottwald 2001, pp ). In addition, there is always a decision to be made about what meaning to represent in logical form and what to leave for linguistic annotation or treatment. For example, so far in our work representing the logic of particular statutes, we have needed to use only the basic, three-valued connectives AND, OR, RULE FACTORS, and UNLESS, and we have left the representation of concepts like negation and quantification for semantic annotation and rules, rather than trying to represent them using logical formalism. Legal rules can be chained together, with a condition of one rule becoming a conclusion of another rule. A system of legal rules is represented as an inverted rule tree, the top or root node of the tree being the ultimate conclusion to be proved, and each level of each branch extending downward from the top node stating the logical conditions for proving the immediately higher proposition. Inferences proceed upward, from the conditions of one rule to its conclusion, which in turn helps (with any sibling propositions on the same level) to determine the truthvalue of its conclusion in the next higher level of the tree. The top conclusion of the rule tree is the ultimate issue to be proved in order for the governmental action to be justified for example, in the case of claims under the VICP, that the petitioner is entitled to compensation under the National Vaccine Injury Compensation Program. Thus, a single rule tree can represent the complete set of process and substantive conditions that must be satisfied before a governmental decision or action can be lawful. Moreover, a rule tree provides the logical form for representing the systems of legal rules that statutes create. 13 The next section will present a portion of the rule tree governing the VICP Substantive Rules: Limiting the Field of Governmental Action This section uses the rule system governing compensation decisions in the VICP to illustrate substantive rules and how they limit the field within which govern- 13 We present here only the semantic elements and a graphical depiction of the logic of a rule tree, for it is straightforward to represent the same information in various symbolic forms. For example, a system of rules can be represented as conditional propositions nested within the conditions of other conditional propositions, with an entire rule tree represented as a single complex conditional. (Note, however, that if the conditional contains a RULE FACTORS connective somewhere within it, it will not be entirely truth-functional.) In addition, the propositions forming a rule tree can be represented as nested elements in an XML file, for data exchange over the Internet.

11 11 mental actors can lawfully take action. The VICP examples also illustrate how the use of rule trees to represent the logical structure of a system of substantive rules can provide a very practical method of organizing evidence and applying these rules. A critical substantive issue in many contested VICP cases is causation : whether the vaccination played a causal role in bringing about the injury or death as alleged by the petitioner. A VICP decision is fair and efficient only if the vaccination did in fact cause the injury (Walker et al. 2013, p. 193). It would be inefficient to use money raised by the vaccine taxes and targeted for vaccine-related injuries to pay for injuries that are unrelated to vaccines. On the other hand, it would be unfair not to pay compensation if the vaccine did in fact causally contribute to the injury, and as a result people might under-utilize vaccines. Congress sought to balance its multiple policy objectives by providing two alternative sets of rules for proving that a vaccine caused an injury: rules for on-table causation (or merely Table causation ) and rules for off-table causation. The first of these two alternative sets of rules governs proving Table causation or causation in Table cases. The statute established an initial Vaccine Injury Table (Table) and conferred authority on the Secretary of HHS to update and maintain the Table through administrative rulemaking (Meyers 2011, p. 799). 14 The Table lists (a) covered vaccines, (b) recognized adverse reactions that might result from the administration of particular vaccines, and (c) recognized time periods in which the first symptom or manifestation of onset must occur after vaccine administration. 15 A petitioner seeking to prove causation in a Table case has the burden of proving (1) that the injury was set forth in the Vaccine Injury Table in association with the vaccine and (2) that the first symptom or manifestation of the onset or of the significant aggravation of the injury occurred within the time period after vaccine administration set forth in the Table. 16 Proving these two conditions to be true triggers a statutory presumption of causation. 17 As we discuss below, this presumption is rebutted if the injury was in fact due to factors unrelated to the administration of the vaccine. A portion of the rule tree representing this presump-tion is shown in Figure U.S.C. 300aa-14 (2011); 42 C.F.R (2011) U.S.C. 300aa-14 (2011) U.S.C. 300aa-11(c)(1)(C)(i) (2011). 17 Shalala v. Whitecotton, 514 U.S. 268, 270 (1995); Grant v. Secretary of the Department of Health and Human Services, 956 F.2d 1144, 1147 (Fed. Cir. 1992); Althen v. Secretary of Health and Human Services, 418 F.3d 1274, 1278 (Fed. Cir. 2005).

12 12 Fig Partial Rule Tree for Vaccine Decisions, Showing the Statutory Presumption of Causation and the Defeating Proposition The second set of rules governs proving causation in fact in off-table or non-table cases.18 This method of proof is available when the petitioner cannot prove one or both of the propositions needed to trigger the statutory presumption of causation.19 In such a case, in order to receive compensation, the petitioner must prove that the injury was caused by the vaccination.20 Because the statute is silent as to the meaning of the phrase was caused by, 21 the Court of Appeals for the Federal Circuit interpreted the meaning, by elaborating sub-rules for proving this statutory requirement. In 2005, the Court in Althen v. Secretary of Health and Human Services, 418 F.3d 1274, 1278 (Fed. Cir. 2005), stated that in off-table cases the petitioner s Shyface v. Secretary of Health and Human Services, 165 F.3d 1344, (Fed. Cir. 1999); Althen, 418 F.3d at 1278; Pafford v. Secretary of Health and Human Services, 451 F.3d 1352, 1355 (Fed. Cir. 2006) U.S.C. 300aa-11(c)(1)(C)(ii) (2011). 20 Id. 21 Shyface, 165 F.3d at ( the statute does not elaborate on the requirement of causation in the proof of a non-table case ). 18

13 13 burden is to show by preponderant evidence that the vaccination brought about her injury by providing: (1) a medical theory causally connecting the vaccination and the injury; (2) a logical sequence of cause and effect showing that the vaccination was the reason for the injury; and (3) a showing of a proximate temporal relationship between vaccination and injury. In interpreting the meaning of the statutory phrase and in elaborating the rules for causation in off-table cases, the Court was guided by its earlier determination that [n]ational uniformity in administration was implicit in Congress purpose with the Vaccine Act, and by its prior holding that a uniform approach, one which implements the statutory purpose, is that of the Restatement (Second) of Torts. 22 If a claimant succeeds in making a prima facie showing of causation in an off-table case, her proof may still be rebutted if the injury was in fact due to factors unrelated to the administration of the vaccine. (Walker et al. 2013, p. 194) The portion of the rule tree representing these three Althen conditions or prongs is shown in Figure Fig Partial Rule Tree for Vaccine Decisions, Showing the Althen Prima Facie Case on Causation and the Defeating Proposition The Federal Circuit elaborated on the first Althen prong (that a medical theory causally connect[s] the vaccination and the injury 23 ) by explaining that it means 22 Id. at Althen, 418 F.3d at This substantive condition derived from Grant, 956 F.2d at 1148; see Shyface, 165 F.3d at 1353.

14 14 that the vaccine can cause the injury. 24 In other words, the first prong has been explained in terms of general causation : whether a medical theory has been advanced by the petitioner that causally links the type of vaccine involved in the particular case to the type of injury alleged. For this reason, as proof under the first Althen prong, a petitioner normally produces a medical expert who testifies about a medical theory, supported by medical or scientific evidence and explanation. The Federal Circuit elaborated on the second Althen prong (that a logical sequence of cause and effect show[s] that the vaccination was the reason for the injury ) by explaining that the petitioner must show that the vaccine was a but-for cause of or the reason for the injury. 25 Often, this might involve showing that the stages of progression (and symptoms, signs, and test results) expected to occur under the medical theory in Althen prong 1 did in fact occur in the petitioner s case. And Althen prong 3 (that there was a proximate temporal relationship between the vaccination and the injury ) is merely a specific instance of actually observing in fact what the medical theory leads us to expect. Thus, Althen s second and third conditions apply the general causal theory of the first condition to the evidence in the specific case. Finally, for all cases, the statute requires a finding that that there is not a preponderance of the evidence that the illness, disability, injury, condition, or death described in the petition is due to factors unrelated to the administration of the vaccine described in the petition. 26 Although the statute did not place the burden of proving this issue on any particular party, the courts have reasonably placed it on the government, thereby interpreting the statute as establishing a defense available to the Secretary of HHS. 27 Moreover, given its placement in the statute, this defense applies to Table as well as off-table cases. 28 We discuss additional aspects of this defense in sections and below Process Rules: Channeling Governmental Discretion While substantive rules identify the relevant issues to be proved in a legal process, such as causation, process rules govern the operation of the process itself. Aside from this distinction between what is to be proved and the process of proving it, however, substantive and process rules share the same logical form as conditional propositions. This means that we can also use rule trees to represent process rules 24 Capizzano v. Secretary of Health and Human Services, 440 F.3d 1317, 1326 (Fed. Cir. 2006). 25 Pafford, 451 F.3d at U.S.C. 300aa-13(a)(1)(B) (2011). 27 See Knudsen v. Secretary of Health and Human Services, 35 F.3d 543, 547 (Fed.Cir. 1994); Althen, 418 F.3d at See 42 U.S.C. 300aa-13(a)(1)(B) (2011); see Grant, 956 F.2d at

15 15 and systems of process rules. Moreover, from a logical perspective, there is an advantage to not needing to draw a formal distinction between substantive and process rules, in avoiding the resulting vagueness of borderline cases. Finally, a balancing of divergent policy objectives can be used to justify adopting process rules, just as they can justify adopting substantive rules. Combining substantive and process rules into a single system is logically straightforward in situations where a statute prescribes both substantive and process conditions for a governmental decision or action. For example, the court might be required to give a defendant due notice of the proceedings, the judge might be required to decide all motions made by parties, and to give correct instructions to the jury. In such situations, we can generally integrate the substantive and process rules merely by joining them as conjuncts of the same rule tree (Walker 2007a, pp ). It is important to keep in mind, however, that an entire rule tree (often containing conjunctions of both substantive and process branches) is ultimately rooted in a single conclusion that warrants some governmental action. Different types of actions will normally be governed by different rule trees. For example, the substantive rules of causation are constituents of the rule tree governing entitlement to compensation under the VICP, and they are necessary conditions for warranting a judicial judgment ordering compensation from the VICP Fund. During the proof process leading to such a conclusion, however, there may be numerous other decisions that the presiding special master must make for example, deciding a motion about the admissibility of certain evidence into the legal record of the proceeding. That decision or action to exclude evidence might be governed by its own set of rules, represented by another rule tree, containing substantive and process rules from the statute that set up the VICP, or from another statute, or from the rules of the court, or from elsewhere. Also, from a practical standpoint, it makes sense to represent such rules separately from the rules governing entitlement decisions, because the same rules on evidence admissibility may be applicable to different decision processes involving different governmental decisions or actions. We should not confuse two distinct points: while we can formally conjoin substantive and process rules into a single tree when appropriate, distinct decisions or actions within the same legal process often require different rule trees representing different sets of rules. The following two sub-sections distinguish and discuss two types of process rules: procedural rules and evidentiary rules Procedural Process Rules Procedural rules govern the dynamics of legal processes by authorizing or requiring decisions that are warranted only at specified periods of time or under specific circumstances. Examples from civil proceedings in federal court are: a defendant

16 16 may move to dismiss for lack of jurisdiction on the basis of the pleadings 29 ; a motion for summary judgment may be filed at any time until 30 days after the close of all discovery 30 ; and motions for directed verdict or for judgment as a matter of law are decided after evidence has been produced at trial (Hazard et al. 2011, 11.19, 11.21). 31 From a logical perspective, the dynamics and timing of a legal process are controlled by the content of the applicable process rules. Rule trees governing such process decisions may themselves also contain substantive conditions to be satisfied for example, in order for summary judgment to be valid it must be true that there is no genuine dispute as to any material fact and the movant is entitled to judgment as a matter of law. 32 The jurisdiction of a federal court provides examples of procedural conditions such as diversity jurisdiction, 33 general federal-question jurisdiction, 34 and admiralty jurisdiction (Hazard et al. 2011, ). 35 The statute establishing the VICP confers jurisdiction on the Court of Federal Claims and the special masters over proceedings to determine whether a petitioner is entitled to compensation under the Program. 36 Petitioners are barred from filing their action in both the Court of Federal Claims and in state court concurrently. 37 Further, the statute gives jurisdiction to the Court of Federal Claims to review a special master s decision, and to: (A) uphold the findings and conclusions of the special master and sustain the special master s decision; (B) set aside any findings of fact or conclusion of law of the special master found to be arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law and issue its own findings of fact and conclusions of law ; or (C) remand the petition to the special master for further action. 38 Another statute grants the Court of Appeals for the Federal Circuit exclusive jurisdiction over an appeal from a final decision of the Court of Federal Claims. 39 After the action is completed in the Court of Federal Claims, petitioners may file a civil action in state or federal court against the vaccine administrator or manufacturer on claims not preempted by the Vaccine Act (Meyers 2011, p. 787) FEDERAL RULE OF CIVIL PROCEDURE 12(b) (2013). 30 FEDERAL RULE OF CIVIL PROCEDURE 56(b) (2013). 31 See FEDERAL RULE OF CIVIL PROCEDURE 50(a) (2013). 32 FEDERAL RULE OF CIVIL PROCEDURE 56(a) (2013) U.S.C (2012) U.S.C (2012) (authorizing actions arising under the Constitution, laws, or treaties of the United States ) U.S.C (2012) U.S.C. 300aa-12 (2011) U.S.C. 300aa-11(a)(2)-(3), 300aa-16(c) (2011) U.S.C. 300aa-12(e)(2)(A)-(C) (2011) U.S.C. 1295(3) (2012). 40 See 42 U.S.C. 300aa-22 (2011).

17 17 Another example of a procedural process rule governing the VICP is the statute of limitations. In the case of vaccine-related injury other than death, petitioner is barred from filing a petition for compensation under the Program more than 36 months after the date of the occurrence of the first symptom or manifestation of onset or of the significant aggravation of such injury. 41 If this rule presents a contested factual issue in a particular case, then a factfinding process might be needed to decide whether the statute of limitations has been satisfied. 42 Finally, an important class of procedural rules are those assigning a burden of production also called a burden of going forward with the evidence (Hazard et al. 2011, 11.12, 11.25). Such a rule imposes upon some particular party, with respect to some particular issue, the burden of developing evidence and introducing it into the legal record in the case. For example, in VICP cases, the burden is on the petitioner to produce evidence on all of the required elements of the petition. 43 If the party with the burden of production fails to produce the minimum amount or quality of evidence that is deemed legally sufficient, then that party should lose on that issue as a matter of law (Hazard et al. 2011, 11.15). The totality of evidence in the record that is relevant to a particular issue is legally sufficient if a factfinder could make reasonable inferences from that evidence to a conclusion or finding on that issue in favor of that party. The presiding judge (as distinct from the factfinder) decides whether a party has satisfied its burden of production, and therefore whether the factfinder should be allowed to assess the evidence and reach a finding (Hazard et al. 2011, 11.15, 11.19). For VICP cases, the Federal Circuit has developed a number of sufficiency-ofevidence rules, establishing that certain types of evidence are insufficient or sufficient as a matter of law to support a legal finding (Walker 2009, p. 33). For example, when proving causation-in-fact in off-table vaccine cases, a temporal association between vaccination and the onset of injury is, by itself, insufficient evidence of causation; nor is it sufficient to establish a mere similarity between a petitioner s injury and an injury listed on the Vaccine Injury Table. 44 As an example of a rule establishing legally sufficient evidence, the Court has held that causation [in fact] can be found in vaccine cases based on epidemiological evidence and the clinical picture regarding the particular child without detailed medical and scientific exposition on the biological mechanisms. 45 Because sufficiency-of-evidence U.S.C. 300aa-16(a)(2) (2011). 42 See, e.g., Cipollone v. Liggett Group, Inc., 893 F.2d 541, 579 (3rd Cir. 1990), aff d in part and rev d in part on other grounds, 499 U.S. 935 (1991) (holding that the district court s grant of summary judgment against the defendants on their statute of limitations defense was inappropriate and that the issue would need to be tried). 43 See 42 U.S.C. 300aa-11(c) (2011). 44 Grant, 956 F.2d at Knudsen v. Secretary of Health and Human Services, 35 F.3d 543, 549 (Fed. Cir. 1994).

18 18 rules establish what counts as sufficient or insufficient evidence as a matter of law, they give reviewing courts the means to set aside findings of fact, without deference to the factfinder. Such rules govern the procedural aspect of the legal process, because rulings of insufficient evidence in response to a motion can curtail the proceeding either before or during trial. Rules such as those in the examples above furnish a means of resolving the substantive issues raised by those motions (e.g., summary judgment s requirement that there be no genuine issue as to any material fact ). These rules also form a natural point of departure for exploring evidentiary process rules, because they establish a floor of evidence (however porous) necessary for the evidence assessment process, which is discussed in the next sub-section Evidentiary Process Rules Evidentiary process rules are rules that help to structure the assessment of the evidence in a particular case, and the inferential process from evidence to conclusions or findings (Walker 2007a, pp ). Examples are rules about what type of evidence is relevant or irrelevant to which issues; rules about admissibility of evidence, either excluding some proffered evidence from the case altogether, or admitting particular items of evidence because they are relevant to some issue in the case 47 ; rules about the standard of proof for the factfinder to use in making findings of fact (Hazard et al. 2011, 11.5, 11.14; Walker 1996, pp , ); and rules allocating the burden of persuasion to particular parties on particular issues, which determine which party loses if the totality of relevant evidence is in equipoise on the proof threshold established by the standard of proof (Hazard et al. 2011, 11.13). All of these rules constrain the factfinder s discretion in assessing the probative value of the evidence and in making findings, and they allow the presiding legal authority to oversee the factfinding process. The following subsections discuss several major categories of evidentiary rules, providing examples from the VICP Relevant-Factor Rules 46 Indeed, by emphasizing the substantive conditions of sufficiency-of-evidence rules, a good argument can be made for considering them as evidentiary process rules instead of procedural process rules. 47 E.g., FEDERAL RULE OF EVIDENCE 407 (2013) (excluding evidence of subsequent measures taken that would have made an earlier injury or harm less likely to occur to prove negligence or a defect in a product, but not requiring exclusion of such evidence when it is offered for another purpose, such as proving the feasibility of precautionary measures ).

19 19 Some rules constrain the discretion of the factfinder by defining relevant evidence and prescribing some applications of that definition. Federal Rule of Evidence 401 defines evidence as being relevant if it has any tendency to make a fact [of consequence in determining the action] more or less probable than it would be without the evidence. Other rules, which we call relevant-factor rules, are rules that prescribe which factual issues or evidence ( factors ) the factfinder either must (compulsory) or may (permissive) consider in making a finding on a particular type of issue. The statute establishing the VICP, for example, establishes the issues that must be proved in order to obtain compensation, by specifying the required contents of a petition and requiring the petitioner to demonstrate those matters by a preponderance of the evidence. 48 The statute then directs that a special master shall consider, in addition to all other relevant medical and scientific evidence contained in the record (A) any diagnosis, conclusion, medical judgment, or autopsy or coroner s report which is contained in the record regarding the nature, causation, and aggravation of the petitioner s illness, disability, injury, condition, or death, and (B) the results of any diagnostic or evaluative test which are contained in the record and the summaries and conclusions. 49 Thus, the statute sets the basic rules for what evidence is relevant in deciding whether to order compensation. Of course, when establishing the necessary elements of a petitioner s prima facie case, the statutory rules do more than merely specify that those elements are relevant: the statute also mandates that proof of all of the elements is a necessary condition for compensation. The rule tree therefore represents the connection of those elements to the ultimate conclusion using the stronger logical connective AND, instead of the weaker connective RULE FACTORS. By contrast, a mere listing of relevant factors (as in the quotation above, stating what a special master shall consider ) is represented using the RULE FACTORS connective discussed in Section 2. Although a relevant-factor rule might specify which types of evidence a factfinder must or may consider in reaching a conclusion on a particular issue, or which types of evidence a factfinder is not allowed to consider, it sometimes provides no guidance on how the factfinder should combine, weigh, or prioritize those factors. Such rules ensure that certain types of evidence are or are not taken into account, without prescribing any formula for reaching a conclusion (in the way that the connectives AND and OR do prescribe formulas). Nevertheless, a U.S.C. 300aa-13(a)(1)(A) (2011) U.S.C. 300aa-13(b)(1) (2011). The Federal Circuit has also provided examples of permissive relevant factors, and has emphasized the probative value of some evidence such as medical opinions of treating physicians. See Capizzano, 440 F.3d at 1326.